Electrical converter



' W. M. BRUBAKER ELECTRICAL CONVERTER Filed June 2, 1947 Oct. 28, 1952ill ATTORNEY INVENTOR Wi/.san M Brubaker.

HC Inbuz WITNESSES: 94. %M

Bu -I- and plate circuits thermore, the output of Patented Oct. 28, 1952ELECTRICAL CONVERTER Wilson M. Bruba-ker, Pitts Westinghouse Electriburgh, Pa., a corpora burgh, Pa., assignor to c Corporation, EastPittstion of Pennsylvania,

Application June 2, 1947, Serial No. 751,876

8 Claims.

This invention relates to devices having outputs representative ofcharacteristics of variable quantities and it has particular relation toa device having an output proportional to the average values of avariable quantity.

In accordance with the invention, a system is provided for establishingtwo electrical currents. One of these currents is increased in magnitudein accordance with alternate half-cycles of an alternating wave. Theremaining electrical current is decreased in magnitude in accordancewith the inverse of the remaining half-cycles of the alternating wave.

In a preferred embodiment of the invention, two electrical tubes areprovided having cathode which are connected in parallel across a powersupply. A control electrode in each of the tubes is associated with aseparate rectifier for energization in accordance with alternatehalf-cycles of an electrical wave. If positive half-cycles of thealternating wave are employed for applying a signal to the controlelectrode of one of the tubes, negative half-cycles are employed forapplying a signal to the: control electrode of the remaining tube. Thecontrol electrodes are energized by the half-cycles with oppositepolarities relative to a common terminal or ground which is connected tothe cathodes of the tubes. Desirably, the amplified prior to itsapplication to rectifiers.

A system embodying the invention has a high input impedance which issubstantially uniform over the entire range of operation thereof. Furthesystem is substanthe average value of the alternating wave is theaforesaid tially linear relative to alternating wave input. 7 As appliedto a symmetrical alternating quantity, the expression average value isintended to denote the half-period average value of the alternatingquantity or quantity resulting from full-wave rectification of thealternating quantity.

It is therefore an object of the invention to provide an improved systemhaving an output representative of the average value of a variablequantity applied thereto.

It is a further object of the invention to provide an electricalconverter for converting an alternating input into a direct currentoutput wherein the system has a high and substantially uniform inputimpedance over the range of op 'eration thereof.

the average value of the wherein the cathodes of all tubes are connectedto one of the input terminals of the system.

It is a still further object of the invention to provide a system fordeveloping twoelectrical currents which are varied in magnitude incpposite directions respectively by successive halfcycles of analternating wave for the purpose of producing an output which isrepresentative of the average value of the alternating wave.

It is an additional object of the invention to provide an improvedmethod for measuring the average value of an alternating wave.

Other objects of the invention will be apparent from the followingdescription of the invention taken in conjunction with the accompanyingdrawing, in which:

Figure l is a schematic view of a vacuum-tube voltmeter;

Fig. 2 is a schematic view of a systemembod'ying the invention forproviding an output representative of the average value of analternating wave;

Fig. 3 is a schematic view showing a modifica tion of the system of Fig.2; and

Fig. 4 is a schematic view showing a modification of a portion of thesystems of Figs. 2 and 3.

Referring to the drawing, Fig. 1 shows a conventional vacuum-tubevoltmeter which includes two tube units or tubes l and3. In the specificembodiment herein illustrated, the tubes comprise triodes, each having acathode element, an anode element and a control electrode or grid. Forexample, the tube I has a cathode element la, an anode element lb and acontrol electrode Ic. Similarly, the tube 3 has a cathode element 3a, ananode element 31) and a control electrode 30. The cathode elements areconnected through a common resistor5 and a common terminal 6 to oneterminal of a source of power 1. Generally, this source of powerrepresents a direct current source. Resistors Id and 3d are connected inseries respectively with the anode elements lb and 3b. The free ends ofthe resistors id and 3d are connected to the terminals of a resistor 9.This resistor has an adjustable tap II which is connected to theremaining terminal of prior art the source of power I.

By an inspection of Fig. 1, it will be observed that the controlelectrode 30 is connected directly to the common terminal 6. The controlelectrode ic is connected through a switch l3 to one of the taps of avoltage divider l5. A direct current input is connected across theterminals of the voltage divider [5. The magnitude of the input isindicated bya measuring instrument M, which may be of thepermanent-magnet, moving-coil type.

Since the vacuum-tube voltmeter of Fig. 1 is well known in the priorart, a further discussion of its construction and operation is believedto be unnecessary. A similar bridge circuit for a vacuum-tube voltmeteris discussed in the Theory and Applications of Electron Tubes by H. J.Reich, page 602. The second edition of this book was published by theMcGraw and Hill Book Company of New York city in 1944.

The vacuum-tube voltmeter illustrated in Fig. 1 is very satisfactory formeasuring directcurrent inputs. It has also been proposed that analternating quantity be rectified for the purpose of charging acapacitor. The voltage across the capacitor then is measured by thevacuum-tube voltmeter of Fig. 1 for the purpose of indicating the peakvalue of the alternating quantity.

If the alternating quantity has the conventional sinusoidalconfiguration, the peak value pf the quantity has a definite relation tothe root-mean-square magnitude of the quantity, and the voltmeter may becalibrated to indicate directly the related root-meanesquare magnitude.However, wave forms encountered in practice-often do not have asinusoidal configuration.

When the wave form of an alternating wave departs .froma sinusoidalconfiguration, the peak value of the wave no longer represents theeffective or *root-mean-square magitude of the wave. As well understoodin the art, root-meansquare values are commonly employed in theengineering field, and systems-are desired which are responsive to suchroot-mean-square values. A system which is responsive to the averagevalue of an alternating wave provides .an output which bears a muchcloserrelat'ion to. the

root-mean-square magnitude of the wave. Such a system is illustrated inFig. 2.

Referring to Fig. 2. it will be observed that the tubes I and 3, thepower source? and the resistors 5, Id, 3d and .9 are associated insubstantially the same relationship discussed with reference to Fig. 5.However, in Fig. 2 the control electrodes I and 3c .are connected to thecommon terminal 6 respectively, through resistors II'and I9.

The switch I-3 and the voltage divider I5 of Fig. 1 again are employedin Fig. 2 for supplying a'suitable input to the tubes I and 3. To this,end the switch .13 is connected to the control electrodes Ia and 3c,respectively, through rec- .tifiers 2I and 23. rectifiers are oppositelypoled. 'Consequently, if vrectifier 2 I is poled to pass positivehalf-cycles It will be noted that the of an input alternating wavethrough the resistor I1, the rectifier 23 is poled to pass negativehalf-cycles of the same alternating wave through the resistor I9. Thedirections of flow of current through the rectifiers 2| and 23 arerepresented respectively by arrows 2Ia and 23a. Consequently, thecurrent represented by the arrow 2Ia energizes the control electrode Icpositivelywith respect to the common terminal 6 whereas the currentrepresented. by the arrow 23a energizes the control electrode 3cnegatively relative to the common terminal 6.

The output from the tubes I and 3 is derived from two terminals I e andSo, which are connected respectively to the anode elements Ib and 3b.Consequently, if an alternating input is connected across the voltagedivider I5 of Fig.

2, the resulting signals on the control electrodes of the tubes tend toincrease the current flowing through the tube I and to decrease thecurrent flowing through the tube 3. For this reason, an output voltageobtained from the two terminals I e and 3e is a pulsating direct voltage which represents the difference in magnitudes between the currentsflowing through the resistors Id and 3d.

Various types of rectifiers may be employed .as the rectifiers 2I and23. Barrier-layer rectifiers, such as copper-oxide or seleniumrectifiers, may be employed at the lower frequencies, but the .lowresulting input impedances and capacitances of such rectifiers renderthem less suitable for rectifying high-frequency inputs.

Crystal .rectifiers, such as those containing a major proportion ofsilicon or germanium. may be employed for the rectifiers 2| and 23.These have good high-frequency performance.

As a still further example of rectifiers, electronic rectifiers of thediode type may be employed. Such rectifiers are "suitable for rectifyinghigh-frequency inputs and result in a desirably high input impedance.

It is believed that the operation of the system of Fig. 2 will beapparent from the foregoing discussion. The tap II is adjusted toprovide zero output from the tubes -I and 3 when no input is appliedacross the voltage divider 1-5. When an input is applied across thevoltage divider I5, the switch I3 is manipulated to the desired range.As previously pointed out, the input is rectified by the rectifiers 2iand .2-3 to energize the electrodes 1 0 and 30 with opposite polaritiesrelative to the common terminal 6. It will be recalled that the commonterminal 6 .is connected to the cathode elements of the tubes throughthe common coupling resistor 5.

As a result of the aforesaid energizations of the control electrodes,current through the tube .I increases during alternate half-cycles ofthe input wave Whereas the current through the tube '3 decreases duringtherremaining halfcycles of the alternating wave. The output from theterminals Ie and 3e represents the difference between these currents orthe average value of the alternating input wave, and may be used for anydesired control operation or for application to a measuring instrumentto indicate the average value.

In high-frequency work, the input to the voltage divider .I5 often isderived from grounded electronic equipment, and it is desirable in manycases to ground one terminal of the voltage divider I5 asindicated inFig. 2. In the system of Fig. 2 the cathode elements of the tubes I and3 are connected to ground through the common'resistor 5, and oneterminal of each of the input resistors I1 and I9 also is connected toground. Under such conditions, it is impossible for the input voltagesto float with respect to ground, and stable operation is assured.Furthermore, such connections help to prevent the development ofexcessive potentials at points of the system relative to ground.

The diode rectifier has a desirably large back resistance and areasonablysmall forward resistance. By connecting the diode rectifier inseries with a stable fixed resistance which is large compared to theforward resistance of the diode rectifier, variations in the effectiveforward resistance of the rectifier do not afiect substantially theoverall resistance of the diode rectifier and thefixed resistance.

may be enclosed in separate resistors 39 and 4|.

4| and I9 and. the capacitor ilo.

If the system is employed for measuring direct-current quantities asshown in Fig. l, the

scale of the measuring instrument is essentially linear. If the systemis employed for measuring alternating quantities as shown in Fig. 2, the

' to the small internal voltage of the diode rectifier resulting fromthe velocity of electrons emitted from the cathode element. A discussionof the efiect of initial velocities of emitted electrons or efiectiveanode voltage is presented in the aforesaid Reich book, pages 35 and 36.

Although separate scales may be provided for direct-current andalternating-current measurements, it is desirable to employ a commonscale for both measurements. The effect of the internal voltage on scaledistribution may be minimized by introducing an amplifier between therectifiers and the voltage divider I5. Such an amplifier is illustratedin Fig. 3 and comprises a tube 21 having a cathode element 21a, an anodeelement 21b and a control electrode 21c.- The cathode element 21a isconnected to the common terminal 6 through a biasing resistor 29 havinga capacitor 3| thereacross. The anode element 21b is connected through aresistor 33 to the positive terminal of the power source 1. A resistor35 connects the control electrode 210 to the common terminal 6, and theswitch 13 is connected to the control electrode 210 through a couplingcapacitor 31. Otherwise, Fig. 3 is similar in most respects to thesystem illustrated in fiers 2| and 23 of Fig. 2 are illustrated in Fig.3 as comprising diode units 2IA and 23A. It will be understood that whentubes or tube units such as diode or triode units are employed, theyenvelopes, or several such units may be enclosed in a single envelope.

Resistors 39 and 4| are illustrated as included in the connectionsbetween the diode units and their respective control electrodes. Ifdesired, capacitors 39a and Ma may be connected across The resistors 39and H divider which supplies If the tube I form in efiect a voltage asuitable input to the tube I.

introduces substantial capacitance across the resistor H, the capacitor39a may be selected to provide a ratio of capacitive reactances acrossthe resistors 39 and H which is substantially equal to the ratio of theresistances of the resistors. Similar comments apply to the resistorscapacitor 43 connects the anode element 27b to the rectifiers 2m and23a. Reasonably satis-- factory performance has been obtained despitethe omission of the capacitors 39a and Ma.

As previously pointed out, the diode rectifiers HA and 23A as employedhave characteristics providing a reasonably linear relationship betweenthe applied voltage and the current flowing through the rectifiersexcept for small values of applied voltage. By amplifying the voltageacross the voltage divider l5 before it is applied to the rectifiers,the range of nonlinearity on the meter end can be reduced to anegligible range. This is desirable for the reason that the provision ofa linear scale on the measuring instrument M permits the measuringinstrument to be employed with the same scale for both alternatingcurrent and direct current inputs.

The system of Fig. 3 has a substantially con- Fig. 2. The recti- Acoupling Capacitor 31 stant input impedance over its entire range ofoperation. The input impedance may be of the order of several megohms.In addition, the system provides adequate overload protection for themeasuring instrument M. Such protection may be afforded by designing theamplifier, the rectifiers or the tubes l and 3 to saturate before theoutput has reached a value which would damage the measuring instrumentM.

As representative of suitable components the tube 21 may be a 6J5 tube.The rectifiers may be provided by a 61-16 tube type, and 6K6 tubes (intriode connection) may be employed for the tubes l and 3. With theforegoing tubes, the following component values are suitable:

.01 microfarads Capacitor 43 .1 microfarads Resistor 35 2 X 10 ohmsResistor 33 5 X 10 ohms Resistor I1 10 ohms Resistor l9 10 ohms Resistor39 10 ohms Resistor 4| 10 ohms If the system of Fig. 3 is to be employedas a vacuum-tube voltmeter, the measuring instrument M may take the formof a permanentmagnet, moving-coil instrument connected between theterminals le and 3e.

If desired the internal voltages introduced by the diode rectifiers ofFigs. 2 and 3 may be compensated by means of compensating voltages asshown in Fig. 4. In Fig. 4, the tubes l and 3, the resistors 51 and i9and the common terminal 6 of Fig. 2 or Fig. 3 are shown. Voltage dropsare produced across resistors DH and D19 respectively by batteries BI!and Eli]. An adjustable portion of the voltage drop across the resistorDH is connected in series with the resistor I! with proper polarity tooppose the internal voltage of the associated rectifier and with propermagnitude for neutralizing the internal voltage. Similarly, a portion ofthe voltage drop across the resistor Di is connected in series with theresistor IE! to compensate for the internal voltage of the rectifierassociated with the tube 3.

Although the invention has been described with reference to certainspecific embodiments thereof, numerous modifications are possible. Theappended claims have been drafted to cover all modifications fallingwithin the spirit and scope or the invention.

I claim as my invention:

1. In an electrical converter, first circuit means .for establishingfirst and second current flows, input means, second circuit means forincreasing the first current fiow in accordance with alternate halfcycles of an alternating quantity applied to the input means, thirdcircuit means for decreasing the second current fiow in accordance withthe remaining half cycles of the alternating quantity, and output meansfor providing an output dependent on the difierence between themagnitudes of the first and second current flows. 2. In an electricalconverter, a first unidirectional device comprising a first cathodeelement, a first anode element, said device in operation when energizedfrom a source of voltage being designed to pass a unidirectional currentbetween the elements, and a first control electrode for controllingcurrent fiow between the elements, a second unidirectional devicecomprising a second cathode element, a second anode element, the secondelements when energized from a source of voltage being designed to passa unidirectional source, said resistors -terminals each connected to thesecond terminal 'one of the tube units,

current therebetween, and a second control electrode for con-trollingcurrent fiow between the second elements, input means, first circuitmeans for energizing the first control electrode relative to the. firstelements to increase current flow between the first elements inaccordance with alternate half cycles of an alternating quantity appliedto the input means, second circuit means for energizing the secondcontrol electrode relative to the second elements to decrease currentflow between the second elements in accordance with the values ofremaining half cycles of. the alternating quantity, and terminal meansfor providing an output differentially responsive to the current flows.

3. In an electrical system, a first electronic tube unit having firstoutput elements efiective when energized from a source of voltage forpassing current therebetween and having a control member for controllingcurrent passing bea tween the output elements effective when energizedfrom a source of voltage, a second electronic tube unit having secondoutput elements for passing current therebetween, said second electronictube unit including a second control member for controlling currentpassing between the second output elements, a pair of terminals, a firstrectifier unit connected to energize the first control member relativeto the first output elements in accordance with alternate cycles of analternating quantity applied to the terminals, a second rectifier unitconnected to energize the second control member relative to the secondoutput elements in accordance with the remaining half cycles of thealternating quantity, said control members being energized to affectoppositely the current flows in the respective tube 'units, andtranslating means difierentially responsive to the current flows.

4. A system as defined in claim 3 wherein said rectifier units comp-risediodes, the system comprising an amplifier connected to apply theamplifier output to the terminals, said amplifier having a gainsufiicient to provide a substantially linear relationship between theinput to the translating means and an alternating input to the amplifierover a substantial part of the range of variation of the alternatinginput for which the system is designed.

5. In an electrical system, a plurality of electrical tube units eachhaving a cathode element, an anode element and a control electrode forcontrolling current flow between the elements,

a direct-current source having first and second resistors each having athe first terminal of the having their remaining terminals, a pair ofterminal connected to tive to an associated one of said elements inaccordance with. alternate half cycles of an alternating quantityapplied to the input: terminals, and second circuit means for energizingthe control electrodes of a second of. saidtube units relative to, anassociated one of. the elements in accordance with the remaining: halfcycles of the alternating quantity applied to the input terminals, saidenergizations being poled to affect oppositely the magnitudes of currentflows between the associated elements.

6. A system as defined in claim 5 wherein the cathode elements of eachof said tube units are connected to the direct-current source and to thecontrol electrodes through a common resistor.

7. In an electrical system responsive to the average value of analternating quantity, a. pair of electrical tube units each having ananode element, a cathode element and a control electrode, a commonresistor connecting the cathode elements to a common terminal, meansincluding connections for maintaining said anode elements at a positivepotential relative to said common terminal, said connections including aseparate resistor element for each of the tube units connected to carrythe current flowing between the elements of the associated tube unit,translating means responsive to the difference in magnitudes of thevoltages across said resistor elements, an input terminal, and a pair ofcircuit arms connected in parallel between the common terminal and theinput terminal, each of said arms including a rectifier and a. resistor,said rectifiers being poled to pass current in opposite directionsbetween the input terminal and the common terminal, said controlelectrodes being connected respectively to said arms at pointsintermediate each rectifier and its associated resistor.

8. A system as defined in claim 7 wherein the rectifiers comprise diodeunits, said system including an amplifier for amplifying an alternatingquantity, said amplifier having connections for applying its outputbetween the input terminal and the common terminal, and the amplifierhaving a gain permitting a substantially linear relationship between theinput to the translating means and the alternating quantity over a majorportion of the range of variation of the alternating quantity for whichthe system is designed.

WILSON M. BRUBAKER.

REFERENCES CI'IVED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

